Trauma of the spine is a major cause of disabling injuries. The treatment of these injuries is dependent upon such factors as associated neurological injuries and whether or not the spine is considered "unstable". Most often, the treatment hinges on this latter point. Although these are some accepted criteria in the literature for assessment of clinical instability, they apply only to acute evaluation and do not consider ongoing biological processes of healing and adaptation. Thus, presently we have no ability to assess temporal progression either towards delayed stability or instability. We propose to investigate the healing of injury to the cervical spine as a function of time, up to six months, using a canine model. In vitro definition of "stable" and "unstable" injuries will first be established. This information will then be used in an in vivo model to produce three injuries of varying severity and a sham. Also at the time of surgery, three 0.8 mm steel ball will be implanted into vertebrae at the injury site and one vertebrae above and below it. Using the techniques of stereo radiography and computer digitization, precise analysis of cervical spinal motion will be done in vivo while healing occurs. Three dimensional stability analyses as well as strength measurements of injured and sham spines will be performed in specimens after sacrifice. Besides analyzing each data set individually, correlations with other data types will also be obtained. The in vivo stability testing will provide continuous biomechanical information about the healing process in one and the same animal. This will result in better clinically relevant criteria for the definition of spinal instability. Close correlation of in vitro and in vivo stability results could suggest a method to monitor healing of spinal structures. Finally, functional spinal unit and individual ligament strength analysis will yield data about the changes in the spinal column components, e.g. vertebrae and ligaments, as function of spinal injury and healing time.